Not sure if we are talking at cross purposes here, I use the 6mm ply for the transverse hull profile frames, there is no bending required for these.
The ply you have, is it exterior or interior? exterior is built up with better adhesives than interior.
Using 6mm ply spaced as I suggested will be fine. I have used this method several times, the largest being on a 4ft model (see Blue Marlin in the masterclass section), and currently on Bourbon Orca in the working vessels section of 'dry dock'.
Remember also that each plank is glued to its neighbour as well as the frame, it really is a strong method of construction. Once built, you may consider coating with epoxy and glass cloth making a good strong hull.
Ian